Modulation switching method, transmission station, and receiving station

ABSTRACT

A modulation switching method performed in a radio communication system is disclosed. In the method, difference information between the first channel quality information fed back from the receiving station and second channel quality information used to determine a modulation method is generated and is sent as control information is sent to the receiving station, with the transmission station. Switch information from the difference information received as the control information and third channel quality information being previous information in the receiving station are acquired, and data signal is demodulated based on the switch information, with the receiving station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application filed under 35 USC111a and 365c of PCT application JP2009/059056, filed May 15, 2009. Theforegoing application is hereby incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a modulation switchingmethod in which a modulation method of a data signal is switched basedon channel quality information, a transmission station, and a receivingstation.

BACKGROUND

Recently, digital communication systems such as HSPA (High Speed PacketAccess), LTE (Long Term Evolution), and the like have been developed.For the HSPA, the LTE, or the like, a technology such as AMC (AdaptiveModulation and Coding scheme) or the like is applied to realize datatransmission which is highly effective and highly reliable.

In the AMC, the MCS (Modulation and Coding Scheme) is conducted. Thatis, in a broad sense, control is conducted to switch a modulationmethod. In detail, the control switches a combination of the modulationmethod and a coding rate. By this control, it is possible to apply theMCS and improve data transmission efficiency while maintaining areceiving quality at a predetermined level.

In the above digital communication system, Japanese Laid-open PatentPublication No. 2007-288676discloses a technology in which a basestation corrects a value of a feedback report received from a mobilestation in response to an elapsed time from the report, and transmissionallocation is controlled based on a corrected valued of the feedbackreport.

Also, Japanese Laid-open Patent Publication No. 2008-236018 discloses atechnology in which the base station measures quality of a propagationpath to the mobile station, sets a resource distribution of multiplecontrol signals in a control resource based on the measured quality ofthe propagation path, and sends the resource distribution to the mobilestation.

Control information transmitted from a transmission station by using thecontrol signals is formed by elements such as the MCS. Since the controlinformation is defined for each user, in accordance with increase of thenumber of control bits per user and the number of users, a radioresource available for sending a data signal is decreased, andtransmission efficiency of the data signal is degraded.

SUMMARY

According to an aspect of the embodiment, there is provided a modulationswitching method performed in a radio communication system in which amodulation method for modulating a data signal is determined andswitched based on first channel quality information fed back from areceiving station, and switch information for switching the modulationmethod of the data signal is sent from a transmission station to thereceiving station, the modulation switching method including generating,with the transmission station, difference information between the firstchannel quality information fed back from the receiving station andsecond channel quality information used to determine the modulationmethod; sending, with the transmission station, the differenceinformation as control information to the receiving station; acquiring,with the receiving station, the switch information from the differenceinformation received as the control information and third channelquality information being previous information in the receiving station;and demodulating, with the receiving station, the data signal based onthe switch information.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of atransmission station;

FIG. 2 is a diagram illustrating a configuration example of a receivingstation;

FIG. 3 is a diagram illustrating a CQI table;

FIG. 4 is a diagram illustrating a TBS table;

FIG. 5 is a diagram illustrating an MCS table;

FIG. 6 is a diagram illustrating a transmission station in a firstembodiment;

FIG. 7 is a diagram illustrating a receiving station in the firstembodiment;

FIG. 8 is a diagram illustrating a transmission station in a secondembodiment;

FIG. 9 is a diagram illustrating a receiving station in the secondembodiment;

FIG. 10 is a diagram illustrating a difference CQI table;

FIG. 11 is a diagram illustrating a transmission station in a thirdembodiment;

FIG. 12 is a diagram illustrating a receiving station in the thirdembodiment;

FIG. 13 is a diagram illustrating a transmission station in a fourthembodiment;

FIG. 14 is a diagram illustrating a receiving station in the fourthembodiment;

FIG. 15 is a diagram illustrating a transmission station in a fifthembodiment; and

FIG. 16 is a diagram illustrating a receiving station in the fifthembodiment.

DESCRIPTION OF EMBODIMENTS

A configuration of a digital communication system using AMC (AdaptiveModulation and Coding scheme) will be described with reference to FIG. 1and FIG. 2.

FIG. 1 is a diagram illustrating a configuration example of atransmission station 10. An RF receiver 11 receives a signal fed backfrom a receiving station 30 (FIG. 2), converts a radio frequency into abaseband, conducts quadrature demodulation and an A/D (analog todigital) conversion, and supplies a control signal decoder 12.

The control signal decoder 12 performs a decoding process for a controlsignal, extracts channel quality information (CQI) which indicatesquality of a radio channel, and supplies the CQI to a CQI fine adjustor13. The CQI is calculated based on SINR (Signal-to-Interference andNoise power Ratio) measured by the receiving station 30 (FIG. 2), sothat BLER (BLock Error Rate) becomes 10% when the data signal of atransmission format corresponding to the CQI is received.

As indicated in a CQI table illustrated in FIG. 3, in LTE (Long TermEvolution), information bit number (Efficiency) may be indicated foreach of 16 CQIs (CQI Indices) in which the information bit number(Efficiency) is transmitted by one modulation symbol with a modulationmethod (Modulation) and a coding rate (Coding Rate×1024). Hereinafter,the CQI fed back from the receiving station 30 (FIG. 2) is calledCQI_(FB).

The CQI fine adjustor 13 conducts a fine adjustment for the CQI_(FB)based on an independent determination, and outputs the CQI_(ADJ).Specifically, first, the CQI fine adjustor 13 converts the CQI_(FB) intoSINR (Signal-to-Interference and Noise power Ratio). Next, the CQI fineadjustor 13 averages the SINR in a time direction, and adjusts the SINRdepending on a difference between a target BLER and an actual BLER.Then, the CQI fine adjustor 13 converts the SINR into CQI_(ADJ).

The MCS selector 14 selects the MCS of the data signal, that is, acombination of the modulation method and the coding rate, based on theCQI_(ADJ). 29 types of MCSs may be defined in the LTE, and one MCS isselected as described below.

The MCS selector 14 refers to the CQI table illustrated in FIG. 3, andacquires the modulation method (Modulation) and the information bitnumber (Efficiency) transmitted by one modulation symbol from CQI_(ADJ).Also, by a scheduler (not shown), a resource block (Resource Block: RB)is determined as a frequency resource used to transmit the data signal.

Next, the MCS selector 14 calculates a tentative value of informationbit number alternatively called TBS (Transport Block Size) by using thenumber of a RB and the information bit number (Efficiency). The TBS isregarded as a size transmitted in a sub-frame and as a time unit of thedata transmission.

Also, a portion of a TBS table in the LTE, in which each of 0 to 26candidates (I_(TBS)) (hereinafter, also called TBS indices) of the TBSare defined for 1 to 110 RBs (N_(PRB)), is illustrated in FIG. 4. TheMCS selector 14 determines a value nearest to a temporary value of theTBS in the number of the RB (N_(PRB)) as a target TBS, and acquires aTBS index (I_(TBS)).

Also, in the LTE, as illustrated in a MCS table in FIG. 5, a modulationorder (Q_(m)) of a modulation method and the TBS index (I_(TBS))correspond to each of 29 types (0 to 28) of MCS indices (I_(MCS)). TheMCS selector 14 refers to the MCS table in FIG. 5, and acquires the MCSindex (I_(MCS)) of 5 bits from the modulation order (Q_(m)) and the TBSindex (I_(TBS)). The MCS selector 14 supplies the MCS index (I_(MCS)) of5 bits to an error correction coder 15, a data modulator 16, and acontrol signal generator 17.

The error correction coder 15 conducts an error correction coding forthe data signal (information bit) so that the coding rate becomes avalue indicated by the MCS. The data modulator 16 conducts datamodulation by the modulation method indicated by the MCS.

The control signal generator 17 generates a control signal by conductingcoding, the data modulation, and the like for control informationincluded in the MCS. A pilot signal generator 18 generates a pilotsignal for demodulating the data signal and the control signal at thereceiving station and to measure the CQI. A channel multiplexer 19multiplexes the data signal, the control signal, and the pilot signal,and generates a signal in a transmission form of a predetermined radioaccess method (OFDMA (Orthogonal Frequency Division Multiple Access) orthe like). An RF transmitter 20 conducts a conversion from a baseband tothe radio frequency by a D/A (Digital to Analog) conversion and aquadrature modulation, and sends a signal of the radio frequency to thereceiving station 30.

FIG. 2 is a diagram illustrating a configuration example of thereceiving station 30. An RF receiver 21 receives a signal sent from thetransmission station 10 (FIG. 1), converts from the radio frequency tothe baseband, conducts the quadrature demodulation and the A/D (Analogto Digital) conversion for the received signal, and supplies thereceived signal to a channel separator 22.

The channel separator 22 conducts a receiving process for apredetermined radio access method (OFDMA or the like). The receivingprocess may be an FFT (Fast Fourier Transform) timing detection, a GI(Guard Interval) elimination, and an FFT process in a case of the OFDMA.The channel separator 22 separates a received signal into a data signal,a control signal, and a pilot signal.

A channel estimator 23 calculates a correlation value between the pilotsignal acquired by the channel separator 22 from the received signal anda known pilot signal, and thereby channel state information (CSI) of theradio channel represented by a complex number is estimated.

A CQI calculator 24 calculates the CQI based on a received SINR which isestimated by using the CSI. Specifically, as previously described, theCQI is calculated so that the BLER becomes 10% when the data signal of atransmission format corresponding to the CQI is received.

A control signal decoder 25 conducts a channel compensation by using theCSI provided from the channel estimator 23 for the control signalseparated from the received signal by the channel separator 22, andfurther conducts data demodulation and an error correction decoding.Thus, the control information (including the MCS) is reproduced.

A channel compensator 26 conducts the channel compensation by using theCSI provided from the channel estimator 23 for the data signal separatedfrom the received signal by the channel separator 22. A data demodulator27 conducts the data demodulation by the modulation method which isindicated by the MCS and provided from the control signal decoder 25. Anerror correction decoder 28 conducts the error correction decoding fordata demodulated by the data demodulator 27, with the coding rate whichis indicated by the MCS and provided from the control signal decoder 25.Thus, a value of the information bit is reproduced and output from theerror correction decoder 28.

A control signal generator 29 conducts the coding, the data modulation,and the like for the control information of the CQI_(FB) or the likewhich is regarded as the CQI and is provided from the CQI calculator 24,and thereby the control signal is generated. An RF transmitter 30conducts the D/A conversion and the quadrature modulation for thecontrol signal, converts from the baseband to the radio frequency, andsends a signal of the radio frequency to the transmission station 10.

Preferred embodiments of the present invention will be described withreference to accompanying drawings.

[a] First Embodiment

A configuration of a radio communication system using an AMC method in afirst embodiment will be described with reference to FIG. 6 and FIG. 7.

<Transmission Station in First Embodiment>

FIG. 6 is a diagram illustrating a configuration of a transmissionstation 10-1 in the first embodiment. In FIG. 6, the transmissionstation 10-1 is illustrated as a radio transmission station. Thetransmission station 10-1 includes a channel quality informationreceiver M1, a modulation method switch M2, a modulator M3, a controlinformation generator M4, and a multiplex transmitter M5. The channelquality information receiver M1 receives channel quality informationwhich is fed back from a receiving station 30-1 in FIG. 7. Themodulation method switch M2 determines the modulation method of the datasignal based on the channel quality information received by the channelquality information receiver M1, and switches to the determinedmodulation method. The modulator M3 modulates the data signal by themodulation method which is switched by the modulation method switch M2.

The control information generator M4 generates difference informationbetween channel quality information which is used by the modulationmethod switch M2 to determine the modulation method, and other channelquality information which is fed back from the receiving station 30-1and is received by the channel quality information receiver M1. Themultiplex transmitter M5 multiplexes the control information providedfrom the control information generator M4 with the modulated data signaland the pilot signal which are provided from the modulator M3, and sendsthe control information to the receiving station 30-1. The receivingstation 30-1 is illustrated as a radio receiving station in FIG. 7.

<Receiving Station in First Embodiment>

FIG. 7 is a diagram illustrating a configuration of the receivingstation 30-1 in the first embodiment. In FIG. 7, the receiving station30-1 includes a separator M6, a channel quality information sending partM7, a demodulator M9, and a switch information acquisition part M8. Theseparator M6 receives a signal, in which the control information ismultiplexed with the modulated data signal, from the transmissionstation 10-1 (FIG. 6). Then, the separator M6 separates the receivedsignal into the control information, the modulated data signal, and thepilot signal. The channel quality information sending part M7 generateschannel quality information of the radio channel transmitting the signalbased on the pilot signal separated from the received signal by theseparator M6, and sends the channel quality information to thetransmission station 10-1 (FIG. 6).

The switch information acquisition part M8 acquires switch informationfrom the difference information reported as the control information andprevious channel quality information of the receiving station 30-1itself. The demodulator M9 demodulates the modulated data signalseparated by the separator M6, in response to the modulation methodindicated in the switch information acquired by the switch informationacquisition part M8.

In the first embodiment, instead of the switch information of themodulation method, the difference information, in which the bit numberis less than that of the switch information, is transmitted from thetransmission station 10-1 to the receiving station 30-1. Accordingly, itis possible to improve transmission efficiency of the data signal.

[b] Second Embodiment

A configuration of a digital communication system using AMC will bedescribed with reference to FIG. 8 and FIG. 9. In the second embodiment,a transmission station 10-2 in FIG. 8 may correspond to a radio basestation, and a receiving station 30-2 in FIG. 9 may correspond to amobile station.

<Transmission Station in Second Embodiment>

FIG. 8 is a diagram illustrating a configuration of the transmissionstation 10-2 in the second embodiment. In FIG. 8, the transmissionstation 10-2 includes an RF receiver 41, a control signal decoder 42, aCQI fine adjustor 43, an MCS selector 44, an error correction coder 45,a data modulator 46, a CQI difference calculator 47, a control signalgenerator 48, a pilot signal generator 49, a channel multiplexer 50, andan RF transmitter 51.

The RF receiver 41 receives a signal which is fed back from thereceiving station 30-2. The RF receiver 41 converts from the radiofrequency to the baseband, and conducts the quadrature demodulation andthe A/D conversion, for the received signal. After that, the RF receiver41 supplies the received signal to the control signal decoder 42.

The control signal decoder 42 extracts the channel quality information(CQI) indicating quality of the radio channel by performing a decodingprocess for the control signal. The CQI is calculated based on thereceived SINR measured by the receiving station 30-2, so that BLER(BLock Error Rate) becomes 10% when the data signal of a transmissionformat corresponding to the CQI is received.

As indicated in the CQI table in FIG. 3, in the LTE, information bitnumber (Efficiency) is indicated for each of 16 CQIs (CQI Indices) inwhich the information bit number (Efficiency) is transmitted by onemodulation symbol with a modulation method (Modulation) and a codingrate (Coding Rate×1024). If CQI=1, the modulation method may be QPSK(Quadrature Phase Shift Keying), the coding rate may be 0.07617(=78/1024), and the number of information bits, which are transmitted byone modulation symbol, may be 0.1523 (=0.07617×2). The control signaldecoder 42 supplies the CQI_(FB), which is fed back from the receivingstation 30-2, to the CQI fine adjustor 43 and the CQI differencecalculator 47.

The CQI fine adjustor 43 conducts the fine adjustment for the CQI_(FB)based on an independent determination, and outputs the CQI_(ADJ).Specifically, first, the CQI fine adjustor 13 converts the CQI_(FB) intoSINR (Signal-to-Interference and Noise power Ratio). Next, the CQI fineadjustor 13 averages the SINR in a time direction, and adjusts the SINRdepending on a difference between a target BLER and an actual BLER.Then, the CQI fine adjustor 43 converts the SINR into CQI_(ADJ).

The MCS selector 44 selects the MCS of the data signal based on theCQI_(ADJ). The modulation method in a broad sense, that is, acombination of the modulation method and the coding rate in detail isselected. In the LTE, 29 types of the MCSs are defined. The MCS isselected as described below.

The MCS selector 44 refers to the CQI table illustrated in FIG. 3, andacquires the modulation method (Modulation) and the information bitnumber (Efficiency) from the CQI_(ADJ). Also, by a scheduler (notshown), a resource block (Resource Block: RB) is determined as afrequency resource used to transmit the data signal.

Next, the MCS selector 44 calculates the temporary value of theinformation bit TBS which is regarded as a time unit and is transmittedin the sub-frame, by using the RB number and the information bit number.

Also, a portion of the TBS table in the LTE, in which each of 0 to 26candidates (I_(TBS)) (TBS indices) of the TBS are defined for 1 to 110RBs (N_(PRB)), is illustrated in FIG. 4. The MCS selector 44 determinesa value nearest to a temporary value of the TBS in the number of the RB(N_(PRB)) as a target TBS, and acquires a TBS index (I_(TBS)).

Also, in the LTE, as illustrated in a MCS table in FIG. 5, a modulationorder (Q_(m)) of a modulation method and the TBS index (I_(TBS)) arecorresponded to each of 29 types (0 to 28) of MCS indices (I_(MCS)). TheMCS selector 44 refers to the MCS table in FIG. 5, and acquires the MCSindex (I_(MCS)) of bits from the modulation order (Q_(m)) and the TBSindex (I_(TBS)). The MCS selector 44 supplies the MCS index (I_(MCS)) of5 bits to an error correction coder 45, and a data modulator 46.

The error correction coder 45 conducts error correction coding for thedata signal (information bits) so that the coding rate becomes a valueindicated by the MCS. The data modulator 46 conducts data modulation bythe modulation method indicated by the MCS.

The CQI difference calculator 47 calculates a difference between theCQI_(ADJ) after the fine adjustment is performed by the CQI fineadjustor 43 and the CQI_(FB) which is fed back most recently, andcalculates information CQI_(DIFF) corresponding to the difference. Thedifference between the CQI_(ADJ) and the CQI_(FB) is related to a timejitter of the radio channel. Thus, the difference is sufficientlysmaller than that in a definition region of the entire CQI.

Accordingly, in a case of the LTE, with respect to the total 16 types ofthe CQIs, 8 types (3 bits) of CQI_(DIFF) may be defined as illustratedin a difference CQI table in FIG. 10. In this case, “CQI_(DIFF)=0”corresponds to “difference=−4”, “CQI_(DIFF)=4” corresponds to“difference=0”, and “CQI_(DIFF)=7” corresponds to “difference=3”. TheCQI difference calculator 47 refers to the difference CQI table in FIG.10 with a difference between the CQI_(ADJ) and the CQI_(FB), andacquires the CQI_(DIFF) of 3 bits. Then, the CQI difference calculator47 supplies the acquired the CQI_(DIFF) of 3 bits to the control signalgenerator 48.

In a related art case, the 29 types of the MCSs are sent by control bits(5 bits) to the receiving station 30. In the second embodiment, theCQI_(DIFF) is sent by the control bits (3 bits) to the receiving station30-2. Therefore, it is possible to reduce the number of the controlbits.

The control signal generator 48 generates the control signal byperforming the coding, the data modulation, and the like for the controlinformation such as the CQI_(DIFF), or the like. The pilot signalgenerator 49 generates the pilot signal for the receiving station 30-2to demodulate the data signal and the control signal and to measure theCQI. The channel multiplexer 50 multiplexes a data signal, a controlsignal, and the pilot signal, and generates a signal of a predeterminedaccess method (OFDMA or the like). The RF transmitter 51 converts fromthe baseband to the radio frequency by conducting the D/A conversion andthe quadrature modulation, and sends a signal of the radio frequency.

<Receiving Station in Second Embodiment>

FIG. 9 is a diagram illustrating a configuration of the receivingstation 30-2 in the second embodiment. In FIG. 9, the receiving station30-2 includes an RF receiver 61, a channel separator 62, a channelestimator 63, a CQI calculator 64, a control signal decoder 65, a CQIreproduction part 66, a CQI_(FB) buffer part 67, an MCS selector 68, achannel compensator 69, a data demodulator 70, an error correctiondecoder 71, a control signal generator 72, and an RF transmitter 73.

The RF receiver 61 receives a signal sent from the transmission station10-2 (FIG. 8). The RF receiver 61 converts from the radio frequency tobaseband and conducts the quadrature demodulation and the A/D conversionfor the received signal. After that, the RF receiver 61 supplies thereceived signal to the channel separator 62.

The channel separator 62 conducts the receiving process for thepredetermined radio access method (OFDMA or the like). The receivingprocess may be the FFT timing detection, a GI elimination, and an FFTprocess in a case of the OFDMA. The channel separator 62 separates areceived signal into the data signal, the control signal, and the pilotsignal.

The channel estimator 63 calculates the correlation value between thepilot signal acquired by the channel separator 62 from the receivedsignal and the known pilot signal, thereby estimating the channel stateinformation (CSI) of the radio channel represented by the complexnumber.

The CQI calculator 64 calculates the CQI based on the received SINRwhich is estimated by using the CSI. Specifically, as previouslydescribed, the CQI is calculated so that the BLER becomes 10% when thedata signal of the transmission format corresponding to the CQI isreceived.

The control signal decoder 65 reproduces the control signal (includingCQI_(DIFF)) and supplies CQI_(DIFF) to the CQI reproduction part 66.

On the other hand, the CQI, which is calculated by the CQI calculator64, is supplied to the control signal generator 72 as the CQI_(FB) to befed back to the transmission station 10-2, and is also additionallystored in the CQI_(FB) buffer part 67. The CQI reproduction part 66refers to the difference CQI table in FIG. 10 by using the CQI_(DIFF)supplied from the control signal decoder 65, and acquires a difference(CQI_(ADJ)−CQI_(FB)) between the CQI_(ADJ) and CQI_(FB).

The CQI reproduction part 66 reads out the CQI_(FB), which has the sametiming as the CQI_(FB) used to calculate CQI_(DIFF) at the transmissionstation 10-2, from the CQI_(FB) buffer part 67. The CQI reproductionpart 66 acquires the CQI_(ADJ) by adding the difference(CQI_(ADJ)−CQI_(FB)) to the CQI_(FB) being read out, and supplies theCQI_(ADJ) to the MCS selector 68. The MCS selector 68 acquires the MCSfrom the CQI_(ADJ) in accordance with the same rule as the MCS selector44 of the transmission station 10-2, and supplies the MCS to the datademodulator 70 and the error correction decoder 71.

The CQI reproduction part 66 recognizes a total process delay T_(PROC)related to the control signal generator 72, the RF transmitter 73, theRF receiver 61, the channel separator 62, and the control signal decoder65 at the receiving station 30-2, and related to the RF receiver 41, thecontrol signal decoder 42, the CQI difference calculator 47, the controlsignal generator 48, the channel multiplexer 50, and the RF transmitter51 at the transmission station 10-2. The CQI reproduction part 66 readsout the CQI_(FB) before for the total process delay T_(PROC) from theCQI_(FB) buffer part 67 to synchronize timing for the CQI_(FB). Apropagation delay in the radio channel may not be a concern since thepropagation delay is sufficiently smaller than a time unit fortransmitting one packet.

The channel compensator 69 conducts the channel compensation by usingthe CSI provided from the channel estimator 63 with respect to thereceived data signal supplied from the channel separator 62. The datademodulator 70 conducts the data demodulation in accordance with themodulation method indicated by the MCS provided from the MCS selector68. The error correction decoder 71 conducts the error correctiondecoding with respect to data demodulated by the data demodulator 70 byusing the coding rate indicated by the MCS from the MCS selector 68,thereby reproducing and outputting the information bit.

The control signal generator 72 conducts the coding, the datamodulation, and the like with respect to the control information such asthe CQI_(FB), or the like received from the CQI calculator 64. The RFtransmitter 73 conducts the D/A conversion and the quadrature modulationfor the control signal, converts from the baseband to the radiofrequency, and sends a signal of the radio frequency to the transmissionstation 10-2.

As described above, even if the number of the control bits is reducedfrom 5 bits to 3 bits, it is possible for the receiving station 30-2 torecognize the MCS and to decode the data signal. Therefore, it ispossible to reduce an overhead due to the control signal, suppressreduction of the radio resources usable for transmitting the datasignal, and to suppress degradation of the transmission efficiency ofthe data signal.

[c] Third Embodiment

In a system in which a frequency scheduling method such as the LTE isapplied, the CQI may be defined for each of frequency sub-bands. Thethird embodiment suitable for this system will be described.

A configuration of the digital communication system using the AMC methodin the third embodiment will be described with reference to FIG. 11 andFIG. 12. In the third embodiment, a transmission station 10-3 in FIG. 11may correspond to the radio base station, and a receiving station 30-3in FIG. 12 may correspond to the mobile station.

<Transmission Station in Third Embodiment>

FIG. 11 is a diagram illustrating a configuration of the transmissionstation 10-3 in the third embodiment. In FIG. 11, parts that are thesame as those illustrated in FIG. 8 are given by the same referencenumbers. The transmission station 10-3 includes the RF receiver 41, thecontrol signal decoder 42, the error correction coder 45, the datamodulator 46, the pilot signal generator 49, the RF transmitter 51, aCQI_(FB) buffer part 81, a CQI fine adjustor 82, a resource allocationcandidate generator 83, a CQI_(ADJ) averaging part 84, a resourceallocation candidate selector 85, a MCS selector 86, a CQI_(FB)averaging part 87, a CQI difference calculator 88, a control signalgenerator 89, and a channel multiplexer 90.

The RF receiver 41 receives a signal which is fed back from a receivingstation 30-3 (FIG. 12). The RF receiver 41 converts from the radiofrequency to the baseband, and conducts the quadrature demodulation andthe A/D conversion, for the received signal. After that, the RF receiver41 supplies the received signal to the control signal decoder 42.

The control signal decoder 42 conducts the decoding process for thecontrol signal, and extracts the channel quality information (CQI)indicating quality of the radio channel.

In this case, a band in this system is divided into multiple frequencysub-bands. The CQI is defined for each of K frequency sub-bands. Each ofK frequency sub-bands includes J resource blocks RB. K denotes aninteger which is 2 or more. J denotes an integer which is 1 or more. TheCQIs for K frequency sub-bands are individually called CQI_(FB,1), . . ., CQI_(FB,K). Then, by a single transmission from the receiving station30-3, the CQI of all frequency sub-bands or the CQI of one or morefrequency sub-bands in which the channel quality is preferable in allfrequency sub-bands is fed back to the transmission station 10-3.

The CQI is calculated based on the received SINR which is measured atthe receiving station 30-3, so that similar to the second embodiment,the BLER becomes 10% when the data signal of the transmission formatcorresponding to the CQI is received.

The control signal decoder 42 supplies the CQI_(FB,1), . . . ,CQI_(F3,K) which are fed back from the receiving station 30-3, to theCQI_(FB) buffer part 81, and the CQI fine adjustor 82. The latestCQI_(FB,1), . . . , CQI_(FB,K) are additionally stored in the CQI_(FB)buffer part 81. The CQI fine adjustor 82 conducts the fine adjustmentfor each of K frequency sub-bands, similar to that conducted by the CQIfine adjustor 43 in the second embodiment. As a result, the CQI fineadjustor 82 supplies CQI_(ADJ,1), . . . , CQI_(ADJ,K) to the averagingpart 84.

The resource allocation candidate generator 83 generates M resourceallocation candidates which are candidate patterns of the frequencysub-bands to be allocated for a next data transmission. M denotes apositive integer. The CQI_(ADJ) averaging part 84 averages, for each ofM resource allocation candidates, values of the CQI (all or part ofCQI_(ADJ,1), . . . , CQI_(ADJ,K)) respective to the frequency sub-bandsto be allocated for a data transmission. As a result, the CQI_(ADJ)averaging part 84 outputs CQI_(ADJ) _(—) _(AVE,1), . . . , CQI_(ADJ)_(—) _(AVE,M). An averaging method may be a method for converting CQIvalues into SINR values, averaging the SINR values, and converting tothe CQI values, or the like.

The resource allocation candidate selector 85 selects one of M resourceallocation candidates, and outputs resource allocation information RAcorresponding to the selected resource allocation candidate andCQI_(ADJ) _(—) _(AVE) _(—) _(SEL) being an averaged CQI value. As aselection method, that is, as a scheduling algorithm, a method forselecting a resource allocation candidate in which the averaged CQIvalue is highest may be used.

The MCS selector 86 selects the MCS based on the CQI_(ADJ) _(—) _(AVE)_(—) _(SEL) provided from the resource allocation candidate selector 85,and supplies the selected MCS to the error correction coder 45 and thedata modulator 46. A selection method may be similar to that conductedby the MCS selector 44 in the second embodiment.

The error correction coder 45 conducts the error correction coding withrespect to the data signal so that the coding rate becomes a valueindicated by the MCS. The data modulator 46 conducts the data modulationin accordance with the modulation method indicated by the MCS.

The CQI_(FB) averaging part 87 reads out the CQI values of one or morefrequency sub-bands corresponding to the resource allocation informationRA from the CQI_(FB) buffer part 81, and outputs CQI_(FB) _(—) _(AVE) asa result of being averaged.

The CQI difference calculator 88 calculates a difference (CQI_(ADJ) _(—)_(AVE) _(—) _(SEL)−CQI_(FB) _(—) _(AVE)) and acquires the informationCQI_(DIFF) corresponding to the difference (CQI_(ADJ) _(—) _(AVE) _(—)_(SEL)−CQI_(FB) _(—) _(AVE)). The CQI_(ADJ) _(—) _(AVE) _(—) _(SEL) issupplied from the resource allocation candidate selector 85 after thefine adjustment is conducted by the CQI fine adjustor 82, and theaveraging is conducted for the frequency sub-bands by the CQI_(ADJ)averaging part 84. The CQI_(FB) _(—) _(AVE) is supplied from theCQI_(FB) averaging part 87 after the averaging is conducted for thefrequency sub-bands fed back from the receiving station 30-3. Similar tothe second embodiment, the CQI difference calculator 88 may acquire theCQI_(DIFF) of 3 bits by referring to the difference CQI table in FIG.10, and may supply the CQI_(DIFF) to the control signal generator 89.

The control signal generator 89 conducts the coding, the datamodulation, and the like with respect to the control informationincluding the CQI_(DIFF) and the resource allocation information RA, andgenerates the control signal. The pilot signal generator 49 generatesthe pilot signal for demodulating the data signal and the controlsignal, and to measure the CQI at the receiving station 30-3.

The channel multiplexer 90 generates the signal of the predeterminedradio access method (OFDMA, or the like) by multiplexing the datasignal, the control signal, and the pilot signal. The data signal ismultiplexed with the frequency sub-band corresponding to the resourceallocation information RA. The RF transmitter 51 performs a conversionfrom the baseband to the radio frequency by conducting the D/Aconversion and the quadrature modulation, and sends a signal of theradio frequency.

In the third embodiment, the CQI_(DIFF) is reported as the controlinformation with the resource allocation information RA, to thereceiving station 30-3. Also, the CQI_(DIFF) may be sent by the controlbits formed by 3 bits to the receiving station 30-3 in the thirdembodiment. Accordingly, it is possible to reduce the number of thecontrol bits.

<Receiving Station in Third Embodiment>

FIG. 12 is a diagram illustrating a configuration of the receivingstation 30-3 in the third embodiment. In FIG. 12, parts that are thesame as those illustrated in FIG. are given by the same referencenumbers. The receiving station 30-3 includes the RF receiver 61, thechannel estimator 63, the channel compensator 69 the data demodulator70, the error correction decoder 71, the control signal generator 72,the RF transmitter 73, a channel separator 91, a CQI calculator 92, acontrol signal decoder 93, a CQI reproduction part 94, a CQI_(FB) bufferpart 95, a CQI_(FB) averaging part 96, and an MCS selector 97.

The RF receiver 61 receives a signal sent from the transmission station10-3 (FIG. 11). The RF receiver 61 converts from the radio frequency tobaseband and conducts the quadrature demodulation and the A/D conversionfor the received signal. After that, the RF receiver 61 supplies thereceived signal to the channel separator 91.

The channel separator 91 conducts the receiving process for thepredetermined radio access method (OFDMA or the like). The receivingprocess may be the FFT timing detection, the GI elimination, and the FFTprocess in the case of the OFDMA. The channel separator 91 separates thereceived signal into the data signal, the control signal, and the pilotsignal. The data signal is acquired from the frequency sub-bandindicated by the resource allocation information RA sent from thecontrol signal decoder 93.

The channel estimator 63 calculates the correlation value between thepilot signal acquired by the channel separator 91 from the receivedsignal and the known pilot signal, thereby estimating the channel stateinformation (CSI) of the radio channel represented by the complexnumber.

The CQI calculator 92 calculates CQI (CQI_(FB,1), . . . , CQI_(FB,K))for each of the frequency sub-bands based on the received SINR estimatedby using the CSI. Specifically, similar to the second embodiment, theCQI is calculated so that the BLER becomes 10% when the data signal ofthe transmission format corresponding to the CQI is received.

The control signal decoder 93 conducts the channel compensation by usingthe CSI provided from the channel estimator 63, and further conducts thedata demodulation and the error correction decoding with respect to thereceived control signal provided from the channel separator 91, therebyreproducing the control information (RA, CQI_(DIFF), or the like). Thecontrol signal decoder 93 supplies the CQI_(DIFF) to the CQIreproduction part 94, and supplies the resource allocation informationRA to the channel separator 91 and the CQI_(FB) averaging part 96.

The CQI_(FB,1), . . . , CQI_(FB,K), which are calculated by the CQIcalculator 92 for each of the frequency sub-bands, are supplied to thecontrol signal generator 72 to feed back to the transmission station10-3, and are also additionally stored in the CQI_(FB) buffer part 95.

The CQI reproduction part 94 reads out CQI_(FB,1), . . . , CQI_(FB,K),which have the same timings as the previously described CQI_(FB,1), . .. , CQI_(FB,K) used when the CQI_(DIFF) is generated at the transmissionstation 10-3 and is supplied from the control signal decoder 93, fromthe CQI_(FB) buffer part 95.

Similar to the second embodiment, the CQI reproduction part 94 reads outthe CQI_(FB) before for the total process delay T_(PROC) of the processdelays at the receiving station 30-3 and the transmission station 10-3,from the CQI_(FB) buffer part 95 to synchronize timing for the CQI_(FB).

The CQI_(FB) averaging part 96 averages the CQI_(FB,1), . . . ,CQI_(FB,K) read from the CQI_(FB) buffer part 95, for the frequencysub-bands corresponding to the resource allocation information RAsupplied from the control signal decoder 93, and outputs the CQI_(FB)_(—) _(AVE).

The CQI reproduction part 94 refers to the difference CQI table in FIG.10 by using the CQI_(DIFF) provided from the control signal decoder 93,and acquires the difference (CQI_(ADJ) _(—) _(AVE) _(—) _(SEL)−CQI_(FB)_(—) _(AVE)). Next, the CQI reproduction part 94 adds the CQI_(FB) _(—)_(AVE) acquired from the CQI_(FB) averaging part 96 to the difference(CQI_(ADJ) _(—) _(AVE) _(—) _(SEL)−CQI _(—) _(AVE)), to acquire theCQI_(ADJ) _(—) _(AVE) _(—) _(SEL).

The MCS selector 97 acquires the MCS from the CQI_(ADJ) _(—) _(AVE) _(—)_(SEL) in accordance with the same rule as that used by the MCS selector86 in the transmission station 10-3 (FIG. 11).

The channel compensator 69 conducts the channel compensation by usingthe CSI provided from the channel estimator 63 with respect to thereceived data signal supplied from the channel separator 91. The datademodulator 70 conducts the data modulation in accordance with themodulation method indicated by the MCS provided from the MCS selector97. The error correction decoder 71 conducts the error correctiondecoding with respect to data demodulated by the data demodulator 70, byusing the coding rate indicated by the MCS provided from the MCSselector 97, to reproduce and output the information bits.

The control signal generator 72 conducts the coding, the datamodulation, and the like with respect to the control information such asCQI_(FB,1), . . . , CQI_(FB,K), or the like for each of the frequencysub-bands provided from the CQI calculator 92, thereby generating thecontrol signal. The RF transmitter 73 conducts the D/A conversion andthe quadrature modulation for the control signal, converts from thebaseband to the radio frequency, and sends the signal of the radiofrequency to the transmission station 10-3.

Thus, even if the control bits are reduced from 5 bits to 3 bits, it ispossible for the receiving station 30-3 to recognize the MCS withoutproblem and to reproduce the data signal.

[d] Fourth Embodiment

A fourth embodiment of the digital communication system, in which theAMC method is applied to an downlink of an LTE system, will be describedwith reference to FIG. 13 and FIG. 14. In the fourth embodiment, atransmission station 10-4 in FIG. 13 may correspond to the radio basestation, and a receiving station 30-4 in FIG. 14 may correspond to themobile station.

<Transmission Station in Fourth Embodiment>

FIG. 13 is a diagram illustrating a configuration of the transmissionstation 10-4 in the fourth embodiment. In FIG. 13, parts that are thesame as those illustrated in FIG. 8 are given by the same referencenumbers. The transmission station 10-3 includes the RF receiver 41, theCQI fine adjustor 43, the MCS selector 44, the error correction coder45, the data modulator 46, the CQI difference calculator 47, the pilotsignal generator 49, the channel multiplexer 50, the RF transmitter 51,an uplink scheduler 100, a control signal decoder 101, and a controlsignal generator 102.

The RF receiver 41 receives a signal which is fed back from thereceiving station 30-4. The RF receiver 41 converts from the radiofrequency to the baseband, and conducts the quadrature demodulation andthe A/D conversion, for the received signal. After that, the RF receiver41 supplies the received signal to the control signal decoder 101.

Considering quality of the radio channel, a transmission requestreceived from the receiving station 30-4, and the like, the uplinkscheduler 100 sends permission to transmit uplink data to the receivingstation 30-4. The control signal decoder 101 decodes a signal receivedfrom the receiving station 30-4, and extracts uplink control informationUCI including the CQI from the decoded signal.

In the LTE, the uplink control information (UCI) is transmitted by usingone of a physical uplink shared channel (PUSCH) and a physical uplinkcontrol channel (PUCCH). Hereinafter, the physical uplink shared channel(PUSCH) is called “uplink shared channel PUSCH”, and the physical uplinkcontrol channel (PUCCH) is called “uplink control channel PUCCH”. Thatis, if there is the transmission permission of the uplink data, theuplink control information UCI is mapped to the uplink shared channelPUSCH with the uplink data, by additionally providing CRC (CyclicRedundancy Check) bits for detecting an error. If there is not thetransmission permission of the uplink data, the uplink controlinformation UCI is mapped to the uplink control channel PUCCH withoutadditionally providing the CRC bits.

The control signal decoder 101 decodes the uplink shared channel PUSCHor the uplink control channel PUCCH based on the transmission permissiongiven by the uplink scheduler 100 before for time T₁, and extracts theCQI_(FB) from the uplink control information UCI. The time T₁ isregarded as a total of process delays of the control signal generator102, the channel multiplexer 50, the RF transmitter 51, and the RFreceiver 41 at the transmission station 10-4; and process delays of theRF receiver 61, the channel separator 62, a control signal decoder 104(FIG. 14), a control signal generator 103 (FIG. 14), and the RFtransmitter 73 at the receiving station 30-4. The control signal decoder101 recognizes the time T.

When an error of the CQI_(FB) of the uplink shared channel PUSCH isdetected, the control signal decoder 101 suppresses outputting theCQI_(FB). On the other hand, when the error of the CQI_(FB) of theuplink shared channel PUSCH is not detected, or when the CQI_(FB) of theuplink control channel PUCCH is acquired, the control signal decoder 101supplies the CQI_(FB) to the CQI fine adjustor 43 and the CQI differencecalculator 47.

The CQI fine adjustor 43 conducts the fine adjustment for the CQI_(FB)based on an independent determination, and outputs the CQI_(ADJ),similar to the second embodiment.

The MCS selector 44 selects the MCS of the data signal, that is, thecombination of the modulation method and the coding rate based on theCQI_(ADJ), and supplies the selected MCS to the error correction coder45, the data modulator 46, and the control signal generator 102, similarto the second embodiment.

The error correction coder 45 conducts the error correction coding withrespect to the data signal so that the coding rate becomes a valueindicated by the MCS. The data modulator 46 conducts the data modulationin accordance with the modulation method indicated by the MCS.

The CQI difference calculator 47 calculates a difference between theCQI_(ADJ) after the fine adjustment is performed by the CQI fineadjustor 43 and the CQI_(FB) which is fed back most recently, calculatesthe information CQI_(DIFF) corresponding to the difference, and suppliesthe information CQI_(DIFF) to the control signal generator 102, similarto the second embodiment.

The control signal generator 102 generates the control signal byconducting the coding, the data modulation, and the like with respect tothe control information such as information related to the transmissionpermission of the uplink data, the MCS, the CQI_(DIFF), or the like.Reliability of the CQI_(DIFF) depends on reliability of the CQI_(FB). Ina case of transmitting the CQI_(FB) via the uplink shared channel PUSCHto the transmission station 10-4, it is possible to detect an error ofthe CQI_(FB) by using the CRC bits. In a case of detecting the error ofthe CQI_(FB) by the control signal decoder 101, the transmission station10-4 conducts a control by the uplink scheduler 100 so as to suppresstransmission of downlink data to the receiving station 30-4 as themobile station. Therefore, a perception gap concerning the MCS may notoccur between the transmission station 10-4 and the receiving station30-4.

When the CQI_(FB) is transmitted via the uplink control channel PUCCH tothe transmission station 10-4, the error of the CQI_(FB) may not bedetected. Thus, if the transmission station 10-4 misdetermines theCQI_(FB), the perception gap concerning the MCS may occur between thetransmission station 10-4 and the receiving station 30-4.

The control signal generator 102 generates the control signal byselecting one of the CQI_(FB) and the MCS. Accordingly, in a first casewhere the CQI_(DIFF) is calculated based on the CQI_(FB) transmitted viathe uplink shared channel PUSCH, the CQI_(DIFF) is reported to thereceiving station 30-4. In a second case where the CQI_(DIFF) iscalculated based on the CQI_(FB) transmitted via the uplink controlchannel PUCCH, the MCS itself is reported to the receiving station 30-4.It is possible for the control signal generator 102 to recognize thefirst case of reporting the CQI_(DIFF) to the receiving station 30-4 orthe second case of reporting the MCS itself to the receiving station30-4, from the transmission permission given by the uplink scheduler 100before the time T₁. By the above described configuration, the perceptiongap concerning the MCS may not occur between the transmission station10-4 and the receiving station 30-4.

The pilot signal generator 49 generates the pilot signal fordemodulating the data signal and the control signal and to measure theCQI at the receiving station 30-4. The channel multiplexer 50 generatesa signal of the predetermined radio access method (OFDMA or the like) bymultiplexing the data signal, the control signal, and the pilot signal.The RF transmitter 51 converts from the baseband to the radio frequencyby performing the D/A conversion and the quadrature modulation, andsends the signal of the radio frequency.

<Receiving Station in Fourth Embodiment>

FIG. 14 is a diagram illustrating a configuration of the receivingstation 30-4 in the fourth embodiment. In FIG. 14, parts that are thesame as those illustrated in FIG. are given by the same referencenumbers. The receiving station 30-4 includes the RF receiver 61, thechannel separator 62, the channel estimator 63, the CQI calculator 64,the CQI reproduction part 66, the CQI_(FB) buffer part 67, the channelcompensator 69, the data demodulator 70, the error correction decoder71, the RF transmitter 73, the control signal generator 103, a controlsignal decoder 104, and an MCS selector 105.

The RF receiver 61 receives a signal sent from the transmission station10-4 (FIG. 13). The RF receiver 61 converts from the radio frequency tobaseband and conducts the quadrature demodulation and the A/D conversionfor the received signal. After that, the RF receiver 61 supplies thereceived signal to the channel separator 62.

The channel separator 62 conducts the receiving process for thepredetermined radio access method (OFDMA or the like). The receivingprocess may be the FFT timing detection, the GI elimination, and the FFTprocess in the case of the OFDMA. The channel separator 62 separates thereceived signal into the data signal, the control signal, and the pilotsignal.

The channel estimator 63 calculates the correlation value between thepilot signal acquired by the channel separator 62 from the receivedsignal and the known pilot signal, thereby estimating the channel stateinformation (CSI) of the radio channel represented by the complexnumber.

The CQI calculator 64 calculates the CQI based on the received SINRwhich is estimated by using the CSI, similar to the second embodiment.The CQI calculated by the CQI calculator 64 is supplied as the CQI_(FB)to be fed back to the transmission station 10-4 to the control signalgenerator 103 and is also additionally stored in the CQI_(FB) bufferpart 67.

The control signal decoder 104 conducts the channel compensation byusing the CSI provided from the channel estimator 63, and furtherconducts the data demodulation and the error correction decoding, withrespect to the received control signal provided from the channelseparator 62, thereby reproducing the control information. The controlsignal decoder 104 extracts information concerning the transmissionpermission of the uplink data from the reproduced control information.Also, by referring to the information concerning the transmissionpermission of time T₂ old (which is maintained in the control signaldecoder 104), the control signal decoder 104 extracts either one of theCQI_(DIFF) and the MCS from the reproduced control information. If theinformation concerning the transmission permission of the time T₂ oldindicates the transmission permission, the CQI_(DIFF) is extracted. Ifthe information indicates transmission non-permission, the MCS isextracted.

The time T₂ is regarded as a total of process delays of the RF receiver61, the channel separator 62, the control signal generator 103, and theRF transmitter 73 at the receiving station 30-4; and process delays ofthe RF receiver 41, the control signal decoder 101, the control signalgenerator 102, the channel multiplexer 50, and the RF transmitter 51 atthe transmission station 10-4. The control signal decoder 104 recognizesthe time T₂.

The control signal decoder 104 acquires the MCS when the CQI_(DIFF) isextracted, similar to the second embodiment. That is, the CQIreproduction part 66 refers to the difference CQI table in FIG. 10 byusing the CQI_(DIFF) supplied from the control signal decoder 65, andacquires the difference (CQI_(ADJ)−CQI_(FB)) between the CQI_(ADJ) andthe CQI_(FB).

The CQI reproduction part 66 reads out CQI_(FB), which is the same asthe CQI_(FB) used to calculate the CQI_(DIFF) at the transmissionstation 10-4, from the CQI_(FB) buffer part 67, acquires the CQI_(ADJ)by adding the CQI_(FB) to the difference (CQI_(ADJ)−CQI_(FB)), andsupplies the CQI_(ADJ) to the MCS selector 105. Similar to the secondembodiment, the CQI reproduction part 66 reads out the CQI_(FB) beforefor the total process delay T_(PROC) of the process delays at thereceiving station 30-3 and the transmission station 10-3, from theCQI_(FB) buffer part 95 to synchronize timing for the CQI_(FB).

When the MCS is extracted by the control signal decoder 104, the controlsignal decoder 104 supplies the extracted MCS to the MCS selector 105.

The MCS selector 105 acquires the MCS from the CQI_(ADJ) in accordancewith the same rule as the MCS selector 44 in the transmission station10-4. Also, the MCS selector 105 selects the MCS acquired from CQI_(ADJ)supplied from the CQI reproduction part 66 if the information concerningthe transmission permission before for the time T₂, which is suppliedfrom the control signal decoder 104, indicates the transmissionpermission. The MCS selector 105 selects the MCS extracted by thecontrol signal decoder 104 if the information indicates the transmissionnon-permission. Then, the MCS selector 105 supplies the selected MCS tothe data demodulator 70 and the error correction decoder 71.

The channel compensator 69 conducts the channel compensation by usingthe CSI provided from the channel estimator 63 with respect to thereceived data signal supplied from the channel separator 62. The datademodulator 70 conducts the data demodulation in accordance with themodulation method indicated by the MCS provided from the MCS selector105. The error correction decoder 71 conducts the error correctiondecoding for demodulated data received from the data demodulator 70, byusing the coding rate indicated by the MCS supplied from the MCSselector 105, thereby reproducing the information bits. Then, theinformation bits are output from the error correction decoder 71.

The control signal generator 103 selects the uplink shared channel PUSCHwhen determining that a transmission is permitted based on theinformation concerning the transmission permission of the uplink data,the information being extracted by and supplied from the control signaldecoder 104. The control signal generator 103 selects the uplink controlchannel PUCCH when determining that the transmission is not permittedbased on the information concerning the transmission permission of theuplink data. After selecting one of the uplink shared channel PUSCH andthe uplink control channel PUCCH, the control signal generator 103generates the control signal by conducting the coding, the datamodulation, and the like for the control information such as theCQI_(FB) or the like provided from the CQI calculator 64. The RFtransmitter 73 conducts the D/A conversion and the quadrature modulationfor the control signal, converts from the baseband to the radiofrequency, and sends a signal of the radio frequency to the transmissionstation 10-4.

As described above, in a case of generating CQI_(DIFF) based on theCQI_(FB) transmitted via the uplink shared channel PUSCH, even if thenumber of the information bits is reduced, it is possible for thereceiving station 30-4 to recognize the MCS and decode the data signal.

[e] Fifth Embodiment

Next, a fifth embodiment, in which the CQI is defined for each of thefrequency sub-bands, and the uplink control information UCI istransmitted via the uplink shared channel PUSCH or the uplink controlchannel PUCCH, will be described.

A configuration of the digital communication system using the AMC methodin the fifth embodiment will be described with reference to FIG. 15 andFIG. 16. In the fifth embodiment, a transmission station 10-5 in FIG. 15may correspond to the radio base station, and a receiving station 30-5in FIG. 16 may correspond to the mobile station.

<Transmission Station in Fifth Embodiment>

FIG. 15 is a diagram illustrating a configuration of the transmissionstation 10-5 in the fifth embodiment. In FIG. 15, parts that are thesame as those illustrated in FIG. 11 or FIG. 13 are given by the samereference numbers. The transmission station 10-5 includes the RFreceiver 41, the error correction coder 45, the data modulator 46, thepilot signal generator 49, the RF transmitter 51, the CQI_(FB) bufferpart 81, the CQI fine adjustor 82, the resource allocation candidategenerator 83, the CQI_(ADJ) averaging part 84, the resource allocationcandidate selector 85, the MCS selector 86, the CQI_(FB) averaging part87, the CQI difference calculator 88, the channel multiplexer 90, theuplink scheduler 100, the control signal decoder 101, and a controlsignal generator 102.

The RF receiver 41 receives a signal which is fed back from thereceiving station 30-5 (FIG. 16). The RF receiver 41 converts from theradio frequency to the baseband, and conducts the quadraturedemodulation and the A/D conversion, for the received signal. Afterthat, the RF receiver 41 supplies the received signal to the controlsignal decoder 101.

Considering the quality of the radio channel, a transmission requestreceived from the receiving station 30-5, and the like, the uplinkscheduler 100 sends a transmission permission of uplink data to thereceiving station 30-5. The control signal decoder 101 decodes a signalreceived from the receiving station 30-5, and extracts the uplinkcontrol information UCI including the CQI from the decoded signal.

The CQI is defined for each of K frequency sub-bands. Each of Kfrequency sub-bands includes J resource blocks RB. K denotes an integerwhich is 2 or more. J denotes an integer which is 1 or more. The CQIsfor K frequency sub-bands are individually called CQI_(FB,1), . . . ,CQI_(FB,K). Then, by a single transmission from the receiving station30-5, the CQI of all frequency sub-bands or the CQI of one or morefrequency sub-bands in which the channel quality is preferable in allfrequency sub-bands is fed back to the transmission station 10-5.

The CQI is calculated based on the received SINR which is measured atthe receiving station 30-5, so that the BLER becomes 10% when the datasignal of the transmission format corresponding to the CQI is received,similar to the second embodiment.

The control signal decoder 101 decodes the uplink shared channel PUSCHor the uplink control channel PUCCH based on the transmission permissiongiven by the uplink scheduler 100 before for time T₁, and extracts theCQI_(FB) from the uplink control information UCI.

In a case in which the error of the CQI_(FB) of the uplink sharedchannel PUSCH is detected, the control signal decoder 101 outputs theCQI_(FB). However, in another case, the control signal decoder 101supplies CQI_(FB,1), . . . , CQI_(FB,K), which are fed back from thereceiving station 30-5, to the CQI_(FB) buffer part 81 and the CQI fineadjustor 82. The latest CQI_(FB,1), . . . , CQI_(FB,K) are additionallystored in the CQI_(FB) buffer part 81. The CQI fine adjustor 82 conductsthe fine adjustment for each of K frequency sub-bands, similar to thatconducted by the CQI fine adjustor 43 in the second embodiment. As aresult, the CQI fine adjustor 82 supplies CQI_(ADJ,1), . . . ,CQI_(ADJ,K) to the averaging part 84.

The resource allocation candidate generator 83 generates the M resourceallocation candidates which are candidate patterns of the frequencysub-bands to be allocated for a next data transmission. The CQI_(ADJ)averaging part 84 averages, for each of M resource allocationcandidates, values of the CQI (all or part of CQI_(ADJ,1), . . . ,CQI_(ADJ,K)) respective to the frequency sub-bands to be allocated forthe data transmission. As a result, the CQI_(ADJ) averaging part 84outputs CQI_(ADJ) _(—) _(AVE,1), . . . , CQI_(ADJ) _(—) _(AVE,M). Anaveraging method may be a method for converting CQI values into SINRvalues, averaging the SINR values, and converting to the CQI values, orthe like.

The resource allocation candidate selector 85 selects one of M resourceallocation candidates, and outputs resource allocation information RAcorresponding to the selected resource allocation candidate andCQI_(ADJ) _(—) _(AVE) _(—) _(SEL) being an averaged CQI value. As aselection method, that is, as a scheduling algorithm, a method forselecting a resource allocation candidate in which the averaged CQIvalue is highest may be used.

The MCS selector 86 selects the MCS based on the CQI_(ADJ) _(—) _(AVE)_(—) _(SEL) provided from the resource allocation candidate selector 85,and supplies the selected MCS to the error correction coder 45 and thedata modulator 46. A selection method may be similar to that conductedby the MCS selector 44 in the second embodiment.

The error correction coder 45 conducts the error correction coding withrespect to the data signal so that the coding rate becomes a valueindicated by the MCS. The data modulator 46 conducts the data modulationin accordance with the modulation method indicated by the MCS.

The CQI_(FB) averaging part 87 reads out the CQI value of the frequencysub-band corresponding to the resource allocation information RA fromthe CQI_(FB) buffer part 81, and outputs CQI_(FB) _(—) _(AVE) as aresult of being averaged.

The CQI difference calculator 88 calculates a difference (CQI_(ADJ) _(—)_(AVE) _(—) _(SEL)−CQI_(FB) _(—) _(AVE)) and acquires the informationCQI_(DIFF) corresponding to the difference (CQI_(ADJ) _(—) _(AVE) _(—)_(SEL)−CQI_(FB) _(—) _(AVE)). The CQI_(ADJ) _(—) _(AVE) _(—) _(SEL) issupplied from the resource allocation candidate selector 85 after thefine adjustment is conducted by the CQI fine adjustor 82, and theaveraging is conducted for the frequency sub-bands by the CQI_(ADJ)averaging part 84. The CQI_(FB) _(—) _(AVE) is supplied from theCQI_(FB) averaging part 87 after the averaging is conducted for thefrequency sub-bands fed back from the receiving station 30-5. Similar tothe second embodiment, the CQI difference calculator 88 may acquire theCQI_(DIFF) of 3 bits by referring to the difference CQI table in FIG.10, and may supply the CQI_(DIFF) to the control signal generator 102.

The control signal generator 102 generates the control signal byconducting the coding, the data modulation, and the like with respect tothe control information such as information related to the transmissionpermission of the uplink data, the MCS, the CQI_(DIFF), or the like.Reliability of the CQI_(DIFF) depends on reliability of the CQI_(FB). Ina case of transmitting the CQI_(FB) via the uplink shared channel PUSCHto the transmission station 10-5, it is possible to detect an error ofthe CQI_(FB) by using the CRC bits. In a case of detecting the error ofthe CQI_(FB) by the control signal decoder 101, the transmission station10-5 conducts a control by the uplink scheduler 100 so as to suppresstransmission of downlink data to the receiving station 30-5 as themobile station. Therefore, a perception gap concerning the MCS may notoccur between the transmission station 10-5 and the receiving station30-5.

When the CQI_(FB) is transmitted via the uplink control channel PUCCH tothe transmission station 10-5, the error of the CQI_(FB) may not bedetected. Thus, if the transmission station 10-5 misdetermines theCQI_(FB), the perception gap concerning the MCS may occur between thetransmission station 10-5 and the receiving station 30-5.

The control signal generator 102 generates the control signal byselecting one of the CQI_(FB) and the MCS. Accordingly, in a first casewhere the CQI_(DIFF) is calculated based on the CQI_(FB) transmitted viathe uplink shared channel PUSCH, the CQI_(DIFF) is reported to thereceiving station 30-5. In a second case where the CQI_(DIFF) iscalculated based on the CQI_(FB) transmitted via the uplink controlchannel PUCCH, the MCS itself is reported to the receiving station 30-5.It is possible for the control signal generator 102 to recognize thefirst case of reporting the CQI_(DIFF) to the receiving station 30-5 orthe second case of reporting the MCS itself to the receiving station30-5, from the transmission permission given by the uplink scheduler 100before the time T₁. By the above described configuration, the perceptiongap concerning the MCS may not occur between the transmission station10-5 and the receiving station 30-5.

The pilot signal generator 49 generates the pilot signal fordemodulating the data signal and the control signal and to measure theCQI at the receiving station 30-5. The channel multiplexer 90 generatesthe signal of the predetermined radio access method (OFDMA or the like)by multiplexing the data signal, the control signal, and the pilotsignal. The data signal is multiplexed with the frequency sub-bandscorresponding to the resource allocation information RA. The RFtransmitter 51 converts from the baseband to the radio frequency byperforming the D/A conversion and the quadrature modulation, and sendsthe signal of the radio frequency.

In the fifth embodiment, the CQI_(DIFF) is reported as the controlinformation with the resource allocation information RA, to thereceiving station 30-5. Also, the CQI_(DIFF) may be sent by the controlbits formed by 3 bits to the receiving station 30-5 in the thirdembodiment. Accordingly, it is possible to reduce the number of thecontrol bits.

<Receiving Station in Fifth Embodiment>

FIG. 16 is a diagram illustrating a configuration of the receivingstation 30-5 in the fifth embodiment. In FIG. 16, parts that are thesame as those illustrated in FIG. 12 or FIG. 14 are given by the samereference numbers. The receiving station 30-5 includes the RF receiver61, the channel estimator 63, the channel compensator 69, the datademodulator 70, the error correction decoder 71, the RF transmitter 73,the channel separator 91, the CQI calculator 92, the CQI reproductionpart 94, the CQI_(FB) buffer part 95, the CQI_(FB) averaging part 96,the control signal generator 103, the control signal decoder 104, andthe MCS selector 105.

The RF receiver 61 receives a signal sent from the transmission station10-5 (FIG. 15). The RF receiver 61 converts from the radio frequency tobaseband and conducts the quadrature demodulation and the A/D conversionfor the received signal. After that, the RF receiver 61 supplies thereceived signal to the channel separator 91.

The channel separator 91 conducts the receiving process for thepredetermined radio access method (OFDMA or the like). The channelseparator 91 separates the received signal into the data signal, thecontrol signal, and the pilot signal. The data signal is acquired fromthe frequency sub-band indicated by the resource allocation informationRA sent from the control signal decoder 104.

The channel estimator 63 calculates the correlation value between thepilot signal acquired by the channel separator 91 from the receivedsignal and the known pilot signal, thereby estimating the channel stateinformation (CSI) of the radio channel represented by the complexnumber.

The CQI calculator 92 calculates CQI (CQI_(FB,1), . . . , CQI_(FB,K))for each of the frequency sub-bands based on the received SINR estimatedby using the CSI. Specifically, similar to the second embodiment, theCQI is calculated so that the BLER becomes 10% when the data signal ofthe transmission format corresponding to the CQI is received.

The control signal decoder 104 conducts the channel compensation byusing the CSI provided from the channel estimator 63, and furtherconducts the data demodulation and the error correction decoding, withrespect to the received control signal provided from the channelseparator 91. By theses operations, the control signal decoder 104reproduces the control information (RA, CQI_(DIFF), the informationconcerning the transmission permission of the uplink data, or the like),supplies the CQI_(DIFF) to the CQI reproduction part 94, and suppliesthe resource allocation information RA to the channel separator 91 andthe CQI_(FB) averaging part 96. In addition, the control signal decoder104 extracts the information concerning the transmission permission ofthe uplink data to the control signal generator 103. Also, by referringto the information concerning the transmission permission of time T₂before (which is maintained in the control signal decoder 104), thecontrol signal decoder 104 extracts one of the CQI_(DIFF) and the MCSfrom the reproduced control information. If the information concerningthe transmission permission of the time T₂ old indicates thetransmission permission, the CQI_(DIFF) is extracted. If the informationindicates transmission non-permission, the MCS is extracted.

CQI_(FB,1), . . . , CQI_(FB,K) for each of the frequency sub-bands,which are calculated by the CQI calculator 92, are supplied to thecontrol signal generator 103 in order to be fed back to the transmissionstation 10-5, and are also additionally stored in the CQI_(FB) bufferpart 95.

The CQI reproduction part 94 reads out CQI_(FB,1), . . . , CQI_(FB,K),which have the same timings as the CQI_(FB,1), . . . , CQI_(FB,K) usedwhen the CQI_(DIFF) is generated at the transmission station 10-5 and issupplied from the control signal decoder 104, from the CQI_(FB) bufferpart 95.

Similar to the second embodiment, the CQI reproduction part 94 reads outthe CQI_(FB) before for the total process delay T_(PROC) of the processdelays at the receiving station 30-5 and the transmission station 10-5,from the CQI_(FB) buffer part 95 to synchronize timing for the CQI_(FB).

The CQI_(FB) averaging part 96 averages the CQI_(FB,1), . . . ,CQI_(FB,K) extracted from the CQI_(FB) buffer part 95 for the frequencysub-bands corresponding to the resource allocation information RAprovided from the control signal decoder 104, and outputs the CQI_(FB)_(—) _(AVE).

The CQI reproduction part 94 refers to the difference CQI table in FIG.10 by using the CQI_(DIFF) supplied from the control signal decoder 104,thereby acquiring the difference (CQI_(ADJ) _(—) _(AVE) _(—)_(SEL)−CQI_(FB) _(—) _(AVE)). Next, the CQI reproduction part 94acquires the CQI_(ADJ) _(—) _(AVE) _(—) _(SEL) by adding the CQI_(FB)_(—) _(AVE) acquired from the CQI_(FB) averaging part 96 to thedifference (CQI_(ADJ) _(—) _(AVE) _(—) _(SEL)−CQI_(FB) _(—) _(AVE))

When the control signal decoder 104 extracts the MCS, the control signaldecoder 104 supplies the extracted MCS to the MCS selector 105.

The MCS selector 105 acquires the MCS from the CQI_(ADJ) _(—) _(AVE)_(—) _(SEL) in accordance with the same rule as the MCS selector 86 inthe transmission station 10-5. Also, the MCS selector 105 selects theMCS acquired from CQI_(ADJ) supplied from the CQI reproduction part 94if the information concerning the transmission permission before for thetime T₂, which is supplied from the control signal decoder 104,indicates the transmission permission. The MCS selector 105 selects theMCS extracted by the control signal decoder 104 if the informationindicates the transmission non-permission. Then, the MCS selector 105supplies the selected MCS to the data demodulator 70 and the errorcorrection decoder 71.

The channel compensator 69 conducts the channel compensation by usingthe CSI provided from the channel estimator 91 with respect to thereceived data signal supplied from the channel separator 91. The datademodulator 70 conducts the data demodulation in accordance with themodulation method indicated by the MCS provided from the MCS selector105. The error correction decoder 71 conducts the error correctiondecoding for demodulated data received from the data demodulator 70, byusing the coding rate indicated by the MCS supplied from the MCSselector 105, thereby reproducing the information bits. Then, theinformation bits are output from the error correction decoder 71.

The control signal generator 103 selects the uplink shared channel PUSCHwhen determining that a transmission is permitted based on theinformation concerning the transmission permission of the uplink data,the information being extracted by and supplied from the control signaldecoder 104. The control signal generator 103 selects the uplink controlchannel PUCCH when determining that the transmission is not permittedbased on the information concerning the transmission permission of theuplink data. After selecting one of the uplink shared channel PUSCH andthe uplink control channel PUCCH, the control signal generator 103generates the control signal by conducting the coding, the datamodulation, and the like for the control information such as theCQI_(FB,1), . . . , CQI_(FB,K) or the like provided from the CQIcalculator 92. The RF transmitter 73 conducts the D/A conversion and thequadrature modulation for the control signal, converts from the basebandto the radio frequency, and sends a signal of the radio frequency to thetransmission station 10-5.

As described above, in a case of generating CQI_(DIFF) based on theCQI_(FB) transmitted via the uplink shared channel PUSCH, even if thenumber of the information bits is reduced, it is possible for thereceiving station 30-5 to recognize the MCS and decode the data signal.

According to the above described embodiments, it is possible to reducethe control bits and improve the transmission efficiency of the datasignal.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment of the presentinvention has been described in detail, it should be understood that thevarious changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A modulation switching method performed in aradio communication system in which a modulation method for modulating adata signal is determined and switched based on first channel qualityinformation fed back from a receiving station, and switch informationfor switching the modulation method of the data signal is sent from atransmission station to the receiving station, the modulation switchingmethod comprising: generating, with the transmission station, differenceinformation between the first channel quality information fed back fromthe receiving station and second channel quality information used todetermine the modulation method; sending, with the transmission station,the difference information as control information to the receivingstation; acquiring, with the receiving station, the switch informationfrom the difference information received as the control information andthird channel quality information being previous information in thereceiving station; and demodulating, with the receiving station, thedata signal based on the switch information.
 2. The modulation switchingmethod according to claim 1, wherein when the first channel qualityinformation is fed back in which an error detection code is additionallyprovided by the receiving station, the transmission station generatesthe difference information between the first channel quality informationfed back from the receiving station and the second channel qualityinformation used to determine the modulation method; and sends thedifference information as the control information to the receivingstation, and when the first channel quality information is fed back inwhich the error detection code is not additionally provided by thereceiving station, the transmission station sends the switch informationas the control information to the receiving station; and wherein whenthe difference information is received as the control information, thereceiving station acquires the switch information from the differenceinformation received from the transmission station and the third channelquality information being the previous information in the receivingstation; and when the switch information is received as the controlinformation, the receiving station extracts the switch information fromthe control information received from the transmission station.
 3. Themodulation switching method according to claim 1, wherein the channelquality information is defined for each of frequency sub-bands, whereinthe transmission station averages the first channel quality informationof the frequency sub-bands fed back from the receiving station for oneor more frequency sub-bands being allocated for a data transmission;generates the difference information between the first channel qualityinformation, which is fed back from the receiving station and isaveraged, and the second channel quality information used to determinethe modulation method; and sends the difference information as thecontrol information to the receiving station; and wherein the receivingstation acquires the switch information based on the differenceinformation received as the control information and an average value offourth channel quality information for the frequency sub-bands allocatedfor the data transmission in the third channel quality information beingprevious information respective to each of the frequency sub-bands.
 4. Atransmission station for determining and switching a modulation methodfor modulating a data signal based on first channel quality informationfed back from a receiving station, and sending switch information forswitching the modulation method of the data signal to the receivingstation, in a radio communication system, the transmission stationcomprising: a receiver configured to receive the first channel qualityinformation fed back from the receiving station; and a transmitterconfigured to transmit difference information between the first channelquality information received by the channel quality information receiverand second channel quality information used to determine the modulationmethod, as control information to the receiving station.
 5. A receivingstation for feeding back first channel quality information to atransmission station and receiving switch information of a modulationmethod of data signal from the transmission station, the modulationmethod being determined and switched by the transmission station basedon the first channel quality information, in a radio communicationsystem, the receiving station comprising: a transmitter configured togenerate the first channel quality information of a radio channel viawhich the data signal is received, and to send the first channel qualityinformation to the transmission station; and a switch informationacquisition part configured to acquire the switch information based ondifference information and third channel quality information beingprevious information in the receiving station, in which the differenceinformation between second channel quality information used to determinethe modulation method and the first channel quality information fed backfrom the receiving station is received from the transmission station asthe control information.
 6. The transmission station according to claim4, wherein the transmitter transmits the difference information, betweenthe first channel quality information received by the receiver and thesecond channel quality information used to determine the modulationmethod, as the control information to the receiving station, when thefirst channel quality information is fed back in which an errordetection code is additionally provided by the receiving station, andsend the switch information as the control information to the receivingstation, when the first channel quality information is fed back in whichthe error detection code is not additionally provided by the receivingstation.
 7. The receiving station according to claim 5, wherein theswitch information acquisition part configured to acquire the switchinformation from the difference information received from thetransmission station and the third channel quality information being theprevious information in the receiving station, when the differenceinformation is received as the control information, and extract theswitch information from the control information received from thetransmission station, when the switch information is received as thecontrol information.
 8. The transmission station according to claim 4,wherein the channel quality information is defined for each of frequencysub-bands, and comprises control information generator configured toaverage the first channel quality information of the frequency sub-bandsfed back from the receiving station for one or more frequency sub-bandsbeing allocated for a data transmission, generate the differenceinformation between the first channel quality information, which is fedback from the receiving station and is averaged, and the second channelquality information used to determine the modulation method, and thetransmitter transmits the difference information as the controlinformation to the receiving station.
 9. The receiving station asclaimed in claim 5, wherein the transmitter transmits first channelinformation generated for each of the frequency sub-bands of the radiochannel via which the data signal is received, to the transmissionstation, and the switch information acquisition part is configured toacquire the switch information based on the difference informationreceived as the control information and an average value of fourthchannel quality information for the frequency sub-bands allocated forthe data transmission in the third channel quality information beingprevious information respective to each of the frequency sub-bands.